hello - I need to create a pro-rata. I have a number of impressions by day, but a total of cost for the month. I want to use the pro rata of my daily impression to have a daily cost. Does anyone know how to do this? thanks Sandra

Sandra welcome to the forums! You really need to give us a few more details. But if you put your date field on the row or column shelf set to MONTH and then create a calculation like this:

SUM([Impressions])/SUM([Cost])

And you this on the row or column shelf, you should get a bar chart showing your cost per impression aggregated to month. This of course depends on how your data is laid out. Is it coming from the same data source or are costs coming from a different data source? What's the linking field for those data sources.

Sandra, it sounds like your data is coming from two different sources. One for the impressions, clicks, etc. aggregated daily and another one that holds your spend or costs aggregated by month. I assumed this to be the case in the attached workbook. The only tricky bit (apart from table calculations in general) is that you need to create this calculation in each data source:

DATENAME('month', [Date] )

And use it as your linking field, NOT the date field. In the secondary data source note the broken (grey) link and the functioning (orange) link, and which is which. After that it is just a matter of setting your compute using fields correctly in the table calculations.